The Audrey Braille Display, 2017

The design has evolved from the original rack and pinion to a wheel design. The wheel combines all 64 possible braille cells patterns into a 64-row wheel about 2 inches across, which means a very compact design is possible. Each cell is driven by a single motor that turns in one direction, making the part count low (for example, no H-bridge for motor control – just a transistor.) Since a regular motor can be much cheaper than a stepper, the result is lower cost – in fact, I’ve estimated I can build it for under $200 for a 20-character device.

In practice, an Arduino will communicate with the computer via USB, and send signals to each motor for positioning. By turning the wheels precisely, any given pattern can be placed under a sensor window, to be touched by the finger.

And three wheels per cell? Packing things together makes for a very tight design. If I had a machine shop that could adhere to ultra precise tolerances for parts, I could possibly fit every cell into a single wheel/gear. But I’m working with a 3D printer, requiring quite a bit more ‘slop’ in the design. Using three gears per cell allows the motors, sensors, and braille wheel to fit together in a design and not get in the way of each adjacent cell.

In any case, the videos below give more details and some insight as to the current state in early 2017 – please excuse the quality.

Right now, the main problem is positioning. Turning the wheel means setting the wheel to one of 64 possible positions, and within 1/2 millimeter or so of each position, for practical use.

So while I am still moving along with it, and ironing out kinks, I thought it was worthwhile at this time to get a progress report out on the Internet.

VIDEO 1: Audrey Braille Display – Cell Design

A first prototype of a single Braille display cell using the three gears, one for driving, one for the positioning sensor, and the third for the Braille pattern. Using three wheels allows the cells to be positioned closer together, since the drive motor would get in the way of adjacent cells if it was in the same position for each cell; instead, it can be alternately positioned high and low and still drive the cell.

VIDEO 2: Audrey Braille Display – First Test of Character Positioning

Testing the character positioning accuracy by sending the same character 10 times to the cell, and checking if the rest position varies each time. As a simple visual test, I’m using the single mark on the sensor wheel that marks a full turn of the wheel – it should appear in the same spot for all ten character displays, and if not, means the positioning needs more work (spoiler alert: the positioning needs more work.) However, for a first try with quick and dirty Arduino code I’m happy with the results…

Hello again David,
It’s interesting to see another design being proposed and based upon some form of encoded braille disk. I well remember the dual rotating disks with the Natesan (India) refreshable braille display.

However, I’m not sure about the introductory statement: “The wheel combines all 64 possible braille cells patterns into a 64-row wheel about 2 inches across, which means a very compact design is possible.”
The wheel dimension does not seem to fit with a nominal braille dot/pin spacing of 0.1 inch, assuming that “across” refers to the wheel’s diameter. Am I missing something here?
Regardless, this “low cost” electro-mechanical design certainly invites further evaluation.

Keith – There’s a lot of overlap possible, so the 64 characters of 3 rows each can actually be combined into a circle of 64 rows, yet if you position on any 3-row section you get a unique Braille character (the images and video show the wheel.) Because of this, the deciding factor is how far apart each row is – I used 2.5mm center-to-center so the whole wheel is 160mm in circumference, or about 50mm in diameter (2 inches)

David – OK, now it’s making sense.
I remember a braille encoded slider that was, in essence, derived by unwrapping a Natesan disk (3-dot half-braille cell). Then the slider length could be reduced by studying overlapped braille pin patterns. As I recall, the reduction factor was 24/10.
But you have a somewhat higher factor of 3 for the 6-dot patterns which is intriguing.

I expect that it may be acceptable to a braille reader, but have you had the opportunity to check the “curvature effect” of the braille cell with a braillist?

I’d have to consult my notes to be sure, but I think the curvature was about .01mm from center row to edge rows. But if that turns out to be awkward for a user, one solution would be to repeat the pattern twice (128 rows) which would double the wheel size, and halve the curvature effect.